1. Field of the Invention
The present invention generally pertains to a method of evaluating the bending capacity of a wire harness (WH) in order to estimate its lifetime under repeated bending. According to the present invention, the lifetime of a wire harness can be simulated or evaluated by performing bend tests with the individual electrical cables constituting the wire harness. The invention also relates to a device adapted to perform such a bend test with the individual electrical cable.
2. Description of Background Information
A wire harness is constituted by a bundle of electrical cables, with typical applications in automobiles. In the latter case, some wire harnesses are employed in opening and closing members, for instance door parts, or in sliding members such as sliding seats, in which case they receive repeated bending forces. In these wire harnesses, the constituent electrical cables are subjected to repeated bending and straining, and are thus prone to frequent breaking.
In order to test the lifetime of a wire harness under repeated bending, a bend-test device such as shown in FIG. 1 is used in the prior art.
The device of FIG. 1 includes a pair of plate members 51 linked by a hinge 52 in a freely openable and closable manner. Both plate members 51 include a hole 51a, through which a wire harness can be passed. The respective end portions of the wire harness WH are passed through a corresponding hole 51a, and the wire harness WH is fixed to the plate members 51 by a fixing means (not shown in the figure). When the plate members 51 are repeatedly opened and closed by e.g. a hydraulic cylinder, the entire wire harness WH is repeatedly bent. The bend test is repeated until each electrical cable forming the wire harness is broken.
However, when a wire harness WH is tested as a bundle of electrical cables, a large-scale bend-test device must be used, whose mechanical movements are usually very slow.
At present, when using a device such as shown in FIG. 1, one bending cycle of a wire harness WH requires about 3 seconds, which is very slow in the context of the present invention.
A main object of the present invention is therefore to provide a bend-test method for evaluating the lifetime of a wire harness under repeated bending, which method can be performed by using a compact and lightly equipped testing device. This object is attained by conceiving a device for bend-testing the individual electrical cables forming a wire harness, and evaluating the wire harness lifetime from the results obtained for each electrical cable.
To this end, there is provided a method of simulating and estimating the minimum lifetime under repeated bending of a wire harness containing a plurality of electrical cables having a respective axis. The method includes selecting at least one electrical cable among a plurality of electrical cables of the wire harness, bend-testing the selected electrical cables individually until it fails, so that a limit number of bending cycles for each selected electrical cable can be obtained separately, and estimating a minimum lifetime under repeated bending for the wire harness on the basis of results obtained for each selected electrical cable.
Preferably, the selecting includes selecting one representative cable among the electrical cables belonging to the same cable category.
Preferably yet, the minimum-lifetime estimating includes choosing the shortest lifetime obtained for the bend-tested electrical cables.
Typically, the bend-testing includes providing two cable holding devices at a predetermined distance apart along the axis of the electrical cable, thereby defining a median point located substantially halfway along the predetermined distance, for each selected electrical cable, holding the selected electrical cable by the two cable holding devices, loading a weight at the median point in a direction perpendicular to the axis of the electrical cable, repeatedly bringing the two holding devices closer to, then farther from, each other, so that the selected electrical cable is reciprocatingly flexed and stretched while the weight is loaded, and repeating the above for each selected electrical cable.
Suitably, the weight-loading includes loading the weight, such as to bias the median point by about one percent, with respect to the length of the predetermined distance.
Further, the weight-loading may include providing the electrical cable with a coating, and providing in the coating a notched portion configured to retain the weight.
The invention also relates to a device for estimating the minimum lifetime under repeated bending for a wire harness containing a plurality of electrical cables having a respective axis. The inventive device is configured to bend-test at least one of the electrical cables individually, until it fails, so that a limit number of bending cycles for each of the electrical cables can be obtained separately.
The device preferably includes two cable holding devices, located at a predetermined distance apart along the axis of the electrical cable and configured to hold the latter, so as to define a median point located substantially halfway along the predetermined distance.
The device further includes a driving mechanism, such that the two cable holding devices can be repeatedly brought closer to, then farther from, each other in a reciprocating manner.
Preferably, the cable holding devices include a corresponding holding member including an elastic material portion configured to hold the electrical cable, such that the elastic material portion prevents the electrical cable from compressive strain.
The device may further include a device for biasing the median point by about one percent, with respect to the length of the predetermined distance.